1. Field of the Invention
The present invention relates to an inkjet printing head substrate, an inkjet printing head and an inkjet printing apparatus, and particularly, to an inkjet printing head substrate, an inkjet printing head and an inkjet printing apparatus which form ink supply openings by dry etching.
2. Description of the Related Art
There is provided a method for manufacturing an inkjet printing head substrate, in which two-step etching processing is executed to a silicon substrate to form ink supply openings thereon. For example, there is known the technology in which first etching is performed onto the silicon substrate by wet etching to form a recessed portion, thus forming a liquid chamber thereon, and next, second etching is performed onto the bottom of the recessed portion by dry etching to form ink supply openings (for example, refer to U.S. Pat. No. 6,534,247).
In dry etching using Bosch process, a forming process of a deposited film, a removal process of the deposited film other than a side face by ions and an etching process by a radical are repeatedly executed to etch a silicon substrate. However, upon forming the ink supply opening by dry-etching the bottom of the recessed portion, since the plasma sheath is formed along the recessed portion, the ion for removing the deposited film is affected in the vicinity of the side wall in the recessed portion. Therefore, the deposited film in a position deviated from a desired position is possibly removed. In this manner, since the removal position of the deposited film continuously deviates on the substrate bottom having the recessed portion, the etching by the radial also is resultantly executed to continuously deviate. As a result, there is a possibility that the etching proceeds with an angle of several degrees. This event is not limited to a case of using Bosch process, but occurs in common to a case of using dry etching of general reactive ion etching (RIE).
As an example of the printing head substrate, there is a structure in which ink supply openings and heat resistive elements are alternately arrayed along the array direction of nozzles. When the structure is formed by the aforementioned etching method, there are some cases where an opening position of the ink supply opening at the substrate end positioned in the inclined surface side of the recessed portion deviates further in the end direction. As a result, it is found that there are some cases where the ink supply opening closer to the substrate end than the heat resistive element has a distance longer from the heat resistive element, and meanwhile, the ink supply opening closer to the center in the ejection opening row has a distance shorter from the heat resistive element. Since ink goes through the ink supply opening penetrating the substrate from a common liquid chamber and is filled into a pressure chamber, as a distance from an end of the ink supply opening to the heat resistive element in the pressure chamber is longer, the flow resistance to the ink is the larger. As a result, there occurs a flow resistance difference between the ink supply opening closer to the end of the substrate and the ink supply opening closer to the center of the substrate. Therefore, when pulse current is applied to the heat resistive element, the ink and the generate air bubbles move to be biased in a direction of the ink supply opening where the flow resistance is small, because of the flow resistance difference. As a result, ink droplets to be ejected result in being ejected to be inclined to the central direction of the ejection opening row.
Meanwhile, in the central section of the substrate, the ink supply opening is opened substantially perpendicularly. Therefore, the distance between the heat resistive element and the ink supply opening is constant and there occurs no resistance difference therebetween, so that ink droplets are ejected straight without occurrence of the bias of the bubble release in the development direction.
That is, the ejection opening close to the substrate end ejects ink droplets in a direction positioned in the substrate central section, and the ejection opening positioned in the substrate central section ejects ink droplets straight. Accordingly, since a landing position of the ink droplet by the ejection opening positioned at the substrate end deviates, there are some cases where image degradation occurs.